Circadian rhythms have been observed in individuals of nearly all major taxonomic categories, including man, yet little is known about the cellular or molecular nature of the biological clock which controls these rhythms. This project is utilizing a biochemical genetic approach in which single gene mutations which alter this clock are used to identify specific biochemical functions or metabolic pathways required for normal clock operation. Recent data we have obtained concerning a possible role for cyclic AMP in controlling the clock will be pursued by studying the effects of mutations which specifically alter cyclic AMP metabolism on clock function. The organism used for this study is Neurospora crassa, whose well-characterized circadian clock has many properties similar to those in other organisms and for which a vast backlog of genetic and biochemical techniques and information is available. The discovery of biochemical oscillations in many areas of intermediary metabolism emphasize the importance of oscillations as an inherent property of biological control systems, while the ubiquity of circadian oscillations, encompassing micro-organisms, higher plants, and higher animals, clearly points out their importance in biological organization.